1. Technical Field
The present invention relates to a method of manufacturing a semiconductor device and more particularly, to a method of manufacturing a semiconductor device including performing laser dicing to form a cutting groove in a multi-layer interconnect.
2. Related Art
In a process of manufacturing a semiconductor device, after a multi-layer interconnect is formed on a wafer, the wafer is diced into individual semiconductor chips. In the related art, the wafer is diced into semiconductor chips by a blade. However, in recent years, a low-dielectric-constant film, particularly, a porous film has been used as an insulating interlayer of the multi-layer interconnect. Since the porous film has low adhesion and low mechanical strength, the porous film peels off during dicing with the blade. Therefore, in recent years, a method has been used in which grooves are formed in the porous film and a portion of the surface of the wafer by laser dicing using laser light and the other portion of the wafer is diced by the blade.
Japanese Unexamined patent publication No. 2006-073910 discloses a structure in which an insulating protective film made of a polyimide resin is formed over portions other than electrodes and an oxide film is formed as the base of a cutting surface that is not sufficiently protected by the protective film. In this way, it is disclosed that it is possible to improve the covering performance of the protective film and prevent chipping in the use of a laser dicing machine.
Japanese Unexamined patent publication No. 2007-173325 discloses an apparatus for manufacturing a semiconductor device including a passivation film that covers a semiconductor integrated circuit and a scribe region. In this document, in order to reduce the warpage of a semiconductor substrate caused by the passivation film, grooves are formed in a lattice shape in the passivation film that is provided on the scribe region.
Japanese Unexamined patent publication No. 2005-166890 discloses a structure in which various films are formed on the surface of a chip invalid region and a polyimide film, which is used as a protective film, is removed among the various films in a process of manufacturing a semiconductor device.
In general, a polyimide film, a kind of protective film, is formed as the uppermost layer of a multi-layer interconnect that is formed on a wafer. However, openings are formed in a portion of the polyimide film and elements, such as electrode pads, are exposed through the openings. Therefore, when the polyimide film is cut by laser light along scribe lines, a scattered material adheres to elements, such as electrodes. In order to solve this problem, a method has been proposed in which a protective film that can be removed by a cleaning solution in the subsequent process is formed on the polyimide film provided on the surface of a multi-layer interconnect so as to cover the entire surface of the wafer and the protective film is cut by laser light from the upper side of the protective film (Japanese Unexamined patent publication No. 2008-130886).
However, even though the protective film is formed in this way, the protective film peels off during a dicing operation with laser light and a scattered material adheres to the elements, which will be described with reference to FIGS. 11A to 12C.
FIGS. 11A to 11C are cross-sectional views schematically illustrating a process of manufacturing a semiconductor device 10. FIGS. 12A to 12C are enlarged views illustrating around the scribe line shown in FIGS. 11A to 11C after a protective film 20 is formed.
The semiconductor device 10 includes a multi-layer interconnect 14 and a polyimide film 18 formed on a wafer 12. In recent years, before a cutting process with laser light is performed, the polyimide film 18 remains on the entire surface of the scribe line, only the region in which, for example, an alignment mark or metal for checking electric characteristics is formed is removed, or the polyimide film on the entire surface of the scribe line is opened, as described in Japanese Unexamined patent publication No. 2005-166890. Here, the structure in which the polyimide film 18 on the entire surface of the scribe line is opened to form a scribe line groove 18a is shown. The protective film 20 is coated on the entire surface of the semiconductor device 10 by a spin coating method. Specifically, the semiconductor device 10 is arranged on a dicing sheet 50, and a protective film application stage (not shown) is loaded with the dicing sheet 50 around the semiconductor device 10 fixed by a ring 52. Then, liquid droplets forming the protective film 20 are dropped from nozzles 54 onto the semiconductor device 10 while the protective film application stage is being rotated, thereby forming the protective film 20 on the entire surface of the semiconductor device 10 (FIGS. 11A and 12A).
Then, laser light 60 is radiated along the scribe line of the semiconductor device 10 having the above-mentioned structure to cut the protective film 20, the multi-layer interconnect 14, and a portion of the wafer 12, thereby forming cutting grooves 10a (FIGS. 11B and 12B). Then, a cleaning solution 72 is supplied from nozzles 70 to the semiconductor device 10 while the dicing sheet 50 is being rotated, thereby cleaning the surface of the semiconductor device 10. During a cutting process with the laser light 60, a scattered material is generated from a member to be cut. However, when the surface of the semiconductor device 10 is covered with the protective film 20, the scattered material is deposited on the protective film 20. Then, the scattered material and the protective film 20 are cleaned by the cleaning solution 72 (FIG. 11C).
However, in the related art, there is an uneven portion in the polyimide film 18, and it is difficult to control uniformity of the thickness of the protective film 20 while following the uneven portion.
When the protective film 20 is formed on the polyimide film 18, there is a step portion, such as the scribe line groove 18a or a pad opening, in the surface of the polyimide film 18, which results in a difference in thickness. In regions other than the opening, the thickness is small, for example, in the range of about 0.1 μm to about 3 μm. The scribe line has a large width of, for example, about 100 μm. Therefore, even when the polyimide film 18 on the entire surface of the scribe line is removed, the thickness of the protective film 20 on the scribe line groove 18a is reduced (FIG. 12A).
In general, the laser absorption ratio of the wafer 12 or the multi-layer interconnect 14 is higher than that of the protective film 20. Therefore, when the semiconductor device 10 is cut by the laser light 60, the protective film 20 is likely to be peeled off by the abrasion of the multi-layer interconnect 14 or the wafer 12 due to the laser light 60 (FIG. 12B). FIG. 12B shows an example in which two portions are cut along the scribe line to form two cutting grooves 10a. As such, when the protective film 20 peels off, a scattered material 24 is adhered to the peeled-off portion. In this case, when the protective film 20 is cleaned by the cleaning solution 72 (see FIG. 11C), it is difficult to clean the scattered material 24 (FIG. 12C). When the scattered material 24 is adhered to the upper surface of the polyimide film 18 or a bonding part, such as a bonding pad, yield is lowered or the reliability of the package is lowered.